Background: Impaired executive functions are among the most widely observed in patients suffering from schizophrenia. The use of self-reported outcomes for evaluating treatment and managing care of these patients has been questioned. The aim of this study was to provide new evidence about the suitability of self-reported outcome for use in this specific population by exploring the internal structure, reliability and external validity of a specific quality of life (QoL) instrument, the Schizophrenia Quality of Life questionnaire (SQoL18).
Design: cross-sectional study.
Inclusion criteria: age over 18 years, diagnosis of schizophrenia according to the DSM-IV criteria.
Data collection: sociodemographic (age, gender, and education level) and clinical data (duration of illness, Positive and Negative Syndrome Scale, Calgary Depression Scale for Schizophrenia); QoL (SQoL18); and executive performance (Stroop test, lexical and verbal fluency, and trail-making test). Non-impaired and impaired populations were defined for each of the three tests. For the six groups, psychometric properties were compared to those reported from the reference population assessed in the validation study.
Results: One hundred and thirteen consecutive patients were enrolled. The factor analysis performed in the impaired groups showed that the questionnaire structure adequately matched the initial structure of the SQoL18. The unidimensionality of the dimensions was preserved, and the internal/external validity indices were close to those of the non-impaired groups and the reference population.
Conclusions: Our study suggests that executive dysfunction did not compromise the reliability or validity of self-reported disease-specific QoL questionnaire.
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